1. Field of the Invention
The present invention relates to an organic electroluminescent (EL) device and a method for fabricating the same, and more particularly, to an organic EL device having an organic field effect transistor and an organic light-emitting diode incorporated therein, and a method for fabricating the same.
2. Description of the Related Art
Organic electroluminescent (EL) devices radiate light by electrical excitation generated by an externally applied electrical field. Among such organic EL devices, organic light-emitting diodes (LEDs) are expected to be widely used for flat-panel display purposes. This is because the organic LED can be fabricated with simplicity, at room temperature, and it can be fabricated over not only a crystalline substrate but also a bendable plastic or glass substrate. The organic LED can be formed over both a crystalline substrate or non-crystalline (amorphous) substrate. However, since transistors for driving organic LEDs are processed at high temperature, it is not easy to fabricate the organic LED over a plastic substrate. Thus, in order to drive an organic LED formed over a plastic substrate, there is a trend to use an organic field effect transistor (FET) that can be processed at low temperature of 100xc2x0 C. or less.
FIG. 1 is a cross-sectional view showing an example of a conventional organic EL device having an organic FET and an organic LED incorporated therein.
Referring to FIG. 1, the conventional organic EL device includes an organic LED 110 and an organic FET 120 incorporated on a single substrate 100.
The organic LED 110 includes a transparent electrode 111, an organic light-emitting layer 112 and a metal electrode 113 sequentially formed on the substrate 100. The organic FET 120 includes a gate electrode 121 formed on the substrate 100, a dielectric layer 122 formed on the gate electrode 121, an organic semiconducting layer 123 formed on the dielectric layer 122 and a source electrode 124 and a drain electrode 125 formed on the dielectric layer 122 at either side of the organic semiconducting layer 123. The drain electrode 125 is connected to the transparent electrode 111 and organic light-emitting layer 112 of the organic LED 110.
The organic EL device operates as follows. An electric field is applied to the organic semiconducting layer 123 by the gate electrode 121 of the organic FET 120. A channel is formed in the organic semiconducting layer 123 between the source electrode 124 and the drain electrode 125 by the applied electric field. Carriers move from the source electrode 124 to the drain electrode 125 through the channel to be injected into the organic light-emitting layer 112 of the organic LED 110. The carriers injected into the organic light-emitting layer 112 are combined to generate excitons. The generated excitons extinguish while emitting light corresponding to a lattice energy gap.
The organic LED 110 is parallel to the organic FET 120 in a horizontal direction, and, due to the positional relationship therebetween, the size of the organic FET 120 undesirably reduces an aperture ratio. In order to overcome the problem of a smaller aperture ratio, it is necessary to increase the light emission intensity of a unit pixel in a display device, which deteriorates a life characteristic of the display device.
To solve the above-described problems, it is an object of the present invention to provide an organic electroluminescent device having an organic field effect transistor and an organic light-emitting diode incorporated therein while having a high aperture ratio.
It is another object of the present invention to provide a method. for fabricating the organic electroluminescent device.
To accomplish the first object of the present invention, there is provided a an organic electroluminescent (EL) device including a substrate, a transparent electrode formed on the substrate, an organic light-emitting layer formed on the transparent electrode, a metal electrode formed on the organic light-emitting layer, a first insulating layer formed on the metal electrode, a gate electrode formed on the first insulating layer, a second insulating layer formed on the gate electrode, an organic semiconducting layer formed on the second insulating layer, a source electrode connected to one end of the organic semiconducting layer on the second insulating layer and connected to the metal electrode, and a drain electrode connected to the other end of the organic semiconducting layer on the second insulating layer.
The substrate is preferably a plastic, glass or crystalline substrate.
The transparent electrode may include indium tin oxide (ITO), indium zinc oxide (IZO) and aluminum zinc oxide (AZO).
The organic light-emitting layer may include an organic monomolecular component or an organic polymeric component.
The metal electrode may include at least one selected from the group consisting of aluminum (Al), magnesium (Mg), calcium (Ca), barium (Ba), lithium (Li), yttrium (Y), ytterbium (Yb), cesium (Cs) and silver (Ag).
The dielectric constant of the first insulating layer is preferably relatively lower than that of the second insulating layer.
The gate electrode may include at least one selected from the group consisting of gold (Ag), palladium (Pd), silver (Ag), platinum (Pt), aluminum (Al), copper (Cu) and titanium (Ti).
The source electrode and the drain electrode may include at least one selected from the group consisting of titanium (Ti), gold (Ag), palladium (Pd), chrome (Cr), platinum (Pt), aluminum (Al), calcium (Ca), barium (Ba), magnesium (Mg), silver (Ag), strontium (Sr) and lithium (Li).
The organic semiconducting layer is preferably either an n-type or a p-type.
According to another aspect of the present invention, there is provided an organic EL device including a metal substrate having a first, bottom surface and a second, top surface, an organic light-emitting layer formed on the first surface of the metal substrate, a transparent electrode formed on the organic light-emitting layer, a first insulating layer formed on the second surface of the metal substrate, a gate electrode formed on the first insulating layer, a second insulating layer formed on the gate electrode, an organic semiconducting layer formed on the second insulating layer, a source electrode connected to one end of the organic semiconducting layer on the second insulating layer and connected to the second surface of the metal substrate, and a drain electrode connected to the other end of the organic semiconducting layer on the second insulating layer.
The metal substrate is preferably formed of aluminum or stainless steel coated with one selected from the group consisting of Al, Ca, Sr, Y, Yb, Li and Mg.
According to still another aspect of the present invention, there is provided an organic EL device including an insulating substrate having a first, bottom surface and a second, top surface, a metal electrode formed on the first surface of the insulating substrate, an organic light-emitting layer formed on the metal electrode, a transparent electrode formed on the organic light-emitting layer, a gate electrode formed on the second surface of the insulating substrate, an insulating layer formed on the gate electrode, an organic semiconducting layer formed on the insulating layer, a source electrode connected to one end of the organic semiconducting layer on the insulating layer and connected to the metal substrate, and a drain electrode connected to the other end of the organic semiconducting layer on the insulating layer.
The insulating substrate is preferably a glass or plastic substrate.
To accomplish the second object of the present invention, there is provided a method for fabricating an organic EL device including the steps of sequentially forming a transparent electrode, an organic light-emitting layer and a metal electrode over a substrate to forming an organic LED, forming a first insulating layer on the metal electrode, forming a gate electrode patterned on a portion of the surface of the first insulating layer, forming a second insulating layer on the first insulating layer and the gate electrode, sequentially patterning the second insulating layer and the first insulating layer to form a via hole partially exposing the surface of the metal electrode, forming a metal electrode layer filling the via hole and covering the second insulating layer, patterning the metal electrode layer to partially expose the surface of the second insulating layer, and forming a source electrode contacting the metal electrode and a drain on the second insulating layer, and forming an organic semiconducting layer on the second insulating layer between the source electrode and the drain electrode.
The organic light-emitting layer is preferably formed of an organic monomolecular material or an organic polymeric material.
Also, the organic light-emitting layer is preferably formed by thermal evaporation, spin coating, pulsed laser deposition, cluster ion beam deposition or sputtering.
The metal electrode is preferably formed by thermal evaporation, spin coating, pulsed laser deposition, cluster ion beam deposition or sputtering.
According to another aspect of the present invention, there is provided a method for fabricating an organic EL device including the steps of providing a metal substrate having a first, bottom surface and a second, top surface, sequentially forming an organic light-emitting layer and a transparent electrode on the first surface of the metal substrate, forming a first insulating layer on the second surface of the metal substrate, forming a gate electrode patterned on a portion of the surface of the first insulating layer, forming a second insulating layer on the first insulating layer and the gate electrode, sequentially patterning the second insulating layer and the first insulating layer to form a via hole partially exposing the surface of the metal substrate, forming a metal electrode layer filling the via hole and covering the second insulating layer, patterning the metal electrode layer to partially expose the surface of the second insulating layer, and forming a source electrode contacting the metal electrode and a drain on the second insulating layer, and forming an organic semiconducting layer on the second insulating layer between the source electrode and the drain electrode.
In step of providing the metal substrate, aluminum or stainless steel coated with one selected from the group consisting of Al, Ca, Sr, Y, Yb, Li and Mg, is preferably used.
According to still another aspect of the present invention, there is provided a method for fabricating an organic EL device including the steps of providing an insulating layer having a first, bottom surface and a second, top surface, sequentially forming a metal electrode, an organic light-emitting layer and a transparent electrode on the first surface of the insulating substrate, forming a gate electrode patterned on a portion of the surface of the insulating layer so as not to cover the via hole, forming an insulating layer on the insulating substrate and the gate electrode, patterning the second insulating layer to expose the via hole of the insulating substrate, forming a metal electrode layer contacting the via hole and covering the insulating layer, patterning the metal electrode layer to partially expose the surface of the insulating layer, and forming a source electrode contacting the metal electrode and a drain on the second insulating layer, and forming an organic semiconducting layer on the insulating layer between the source electrode and the drain electrode.
In step of providing the insulating layer, a glass or plastic substrate having a via hole is preferably used.
The present invention is characteristic in that the organic LED and the organic FET for driving the same are vertically incorporated. Thus, the aperture ratio can be noticeably improves, reducing the luminous area, thereby increasing the life cycle of the device.